ETSI TS 102 250-8-1 V1.1.1 (2018-12)

Speech and multimedia Transmission Quality (STQ); QoS aspects for popular services in mobile networks; Part 8: Formalized definition of Quality of Service parameters and their computation; Sub-part 1: General aspects and terminology

DTS/STQ-00218m

General Information

• Status: Published
• Publication Date: 20-Dec-2018
• Technical Committee: STQ MOBILE - STQ Mobile
• Current Stage: 12 - Completion
• Due Date: 04-Jan-2019
• Completion Date: 21-Dec-2018

Standards Content (Sample)

TECHNICAL SPECIFICATION
Speech and multimedia Transmission Quality (STQ);
QoS aspects for popular services in mobile networks;
Part 8: Formalized definition of Quality of Service parameters
and their computation;
Sub-part 1: General aspects and terminology

2 ETSI TS 102 250-8-1 V1.1.1 (2018-12)

Reference
DTS/STQ-00218m
Keywords
3G, GSM, network, QoS, service, speech
ETSI
650 Route des Lucioles
F-06921 Sophia Antipolis Cedex - FRANCE

Tel.: [phone]  Fax: [phone]

Siret N° 348 623 562 00017 - NAF 742 C
Association à but non lucratif enregistrée à la
Sous-Préfecture de Grasse (06) N° 7803/88

Important notice
The present document can be downloaded from:
http://www.etsi.org/standards-search
The present document may be made available in electronic versions and/or in print. The content of any electronic and/or
print versions of the present document shall not be modified without the prior written authorization of ETSI. In case of any
existing or perceived difference in contents between such versions and/or in print, the only prevailing document is the
print of the Portable Document Format (PDF) version kept on a specific network drive within ETSI Secretariat.
Users of the present document should be aware that the document may be subject to revision or change of status.
Information on the current status of this and other ETSI documents is available at
https://portal.etsi.org/TB/ETSIDeliverableStatus.aspx
If you find errors in the present document, please send your comment to one of the following services:
https://portal.etsi.org/People/CommiteeSupportStaff.aspx
Copyright Notification
No part may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying
and microfilm except as authorized by written permission of ETSI.
The content of the PDF version shall not be modified without the written authorization of ETSI.
The copyright and the foregoing restriction extend to reproduction in all media.

© ETSI 2018.
All rights reserved.
TM TM TM
DECT , PLUGTESTS , UMTS and the ETSI logo are trademarks of ETSI registered for the benefit of its Members.
TM TM
3GPP and LTE are trademarks of ETSI registered for the benefit of its Members and
of the 3GPP Organizational Partners.
oneM2M™ logo is a trademark of ETSI registered for the benefit of its Members and
of the oneM2M Partners. ®
GSM and the GSM logo are trademarks registered and owned by the GSM Association.
ETSI
3 ETSI TS 102 250-8-1 V1.1.1 (2018-12)
Contents
Intellectual Property Rights . 6
Foreword . 6
Modal verbs terminology . 6
Introduction . 6
1 Scope . 8
2 References . 8
2.1 Normative references . 8
2.2 Informative references . 10
3 Definitions of terms, symbols and abbreviations . 10
3.1 Terms . 10
3.2 Symbols . 10
3.3 Abbreviations . 11
4 QoS parameter basics . 12
4.1 Measurable quantities and sample averages . 12
4.2 Points of observation . 13
4.3 Events . 14
4.3.1 Introduction. 14
4.3.2 Abstract events . 14
4.3.3 Technical events . 15
4.3.4 Representations of an event at different points of observation . 15
4.3.5 Two-stage specification of QoS parameters defined in terms of events . 16
4.4 Transactions and their trigger events . 16
5 Symbols and formulas for common types of QoS parameters . 17
5.1 Introduction . 17
5.2 Basic measurable quantities associated with events . 17
5.2.1 Event indicators . 17
5.2.2 Event times . 17
5.3 Generic aggregation formulas for sample averages . 17
5.3.1 Introduction. 17
5.3.2 Event count . 18
5.3.3 Sample average . 18
5.3.4 Conditional sample average . 18
5.4 Ratios . 18
5.4.1 Sample ratio of an event . 18
5.4.2 Conditional ratio of an event. 19
5.4.3 Success ratio of a transaction . 19
5.4.4 Failure ratio of a transaction . 19
5.5 Durations . 20
5.5.1 Duration of a transaction . 20
5.5.2 Mean duration of a transaction . 20
5.6 Data amount and data rates. 20
5.6.1 Data amount transferred in a transaction . 20
5.6.2 Data rate of a transaction . 21
5.6.3 Mean data rate of a transaction . 21
6 Phases of service usage and associated QoS parameters . 21
6.1 Segmentation into phases . 21
6.2 Success of a phase . 22
6.3 Duration of a phase. 22
6.4 Other QoS parameters related to a phase . 23
7 Points of observation . 23
7.1 Overview . 23
7.1.1 GERAN/UTRAN/E-UTRAN network access model . 23
ETSI
4 ETSI TS 102 250-8-1 V1.1.1 (2018-12)
7.1.2 2G CS domain . 24
7.1.3 2G PS control plane . 25
7.1.4 2G PS user plane . 25
7.1.5 3G CS domain and PS control plane . 26
7.1.6 3G PS user plane . 27
7.1.7 4G PS control plane . 28
7.1.8 4G PS user plane . 29
7.2 Reference points and associated points of observation . 29
7.2.1 GSM/UMTS/LTE reference point R. 29
7.2.1.1 Specification of the reference point. 29
7.2.1.3 DL@R . 30
7.2.1.4 IMAP4@R . 30
7.2.1.5 POP3@R . 30
7.2.1.6 SMTP@R . 30
7.2.1.7 MLME@R . 30
7.2.1.8 MIC@R . 30
7.2.1.9 SPEAKER@R. 31
7.2.1.10 CAMERA@R . 31
7.2.1.11 VIDEO@R . 31
7.2.1.12 DNS@R . 31
7.2.1.13 FTP@R . 31
7.2.1.14 SIP@R . 31
7.2.1.15 RTP@R . 32
7.2.1.16 RTCP@R . 32
7.2.1.17 RTSP@R . 32
7.2.1.18 HTTP@R . 32
7.2.1.19 DHCP@R . 32
7.2.2 TETRA reference point RT . 33
7.2.2.1 Specification of the reference point. 33
7.2.2.2 AT@RT . 33
7.2.2.3 AUDIO@RT . 33
7.2.3 GSM interface Um . 33
7.2.3.1 Specification of the interface. 33
7.2.3.2 L3NAS@GSM_Um . 33
7.2.3.3 L3AS@GSM_Um . 33
7.2.3.4 RR_PH@GSM_Um . 33
7.2.4 TETRA interface Um. 33
7.2.4.1 Specification of the interface. 33
7.2.4.2 SNDCP@TETRA_Um . 34
7.2.4.3 CMCE@TETRA_Um . 34
7.2.4.4 LLC@T ET RA_U m . 34
7.2.5 UMTS interface Uu . 34
7.2.5.1 Specification of the interface. 34
7.2.5.2 L3NAS@UMTS_Uu . 34
7.2.5.3 L3AS@UMTS_Uu . 34
7.2.6 LTE interface Uu . 34
7.2.6.1 Specification of the interface. 34
7.2.6.2 L3NAS@LTE_Uu . 34
7.2.6.3 L3AS@LTE_Uu . 35
7.2.7 ISDN user network interface (UNI) . 35
7.2.7.1 Specification of the interface. 35
7.2.7.2 DSS1@UNI. 35
Annex A (informative): Example for applying the formulas of clause 5 . 36
A.1 A fictitious service and its QoS parameters . 36
A.2 Elementary measurement data . 36
A.3 Calculated quantities per measurement cycle. 37
A.4 Aggregations/Sample averages . 37
ETSI
5 ETSI TS 102 250-8-1 V1.1.1 (2018-12)
Annex B (informative): Guidelines and templates for specification . 38
B.1 Document structure . 38
B.2 Top-down approach for deriving QoS parameter definitions . 38
B.3 Specification of points of observation . 39
B.3.1 Guidelines. 39
B.3.2 Specification template . 39
B.4 Specification of events . 40
B.4.1 Guidelines. 40
B.4.2 Specification template . 40
B.5 Specification of phases . 40
B.5.1 Guidelines. 40
B.5.2 Specification template . 41
B.6 Specification of QoS parameters . 41
B.6.1 Guidelines. 41
B.6.2 Specification template . 42
History . 43

ETSI
6 ETSI TS 102 250-8-1 V1.1.1 (2018-12)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (https://ipr.etsi.org/).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
Foreword
This Technical Specification (TS) has been produced by ETSI Technical Committee Speech and multimedia
Transmission Quality (STQ).
The present document is part 8, sub-part 1 of a multi-part deliverable. Full details of the entire series can be found in
part 1 [36].
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Introduction
The definition of quality of service (QoS) parameters and their computation, as in ETSI TS 102 250-2 [i.1], involves a
couple of formal aspects which require special attention but have not been addressed systematically so far by the ETSI
TS 102 250 document series. These aspects include:
• Introduction and consistent usage of appropriate symbols in mathematical equations according to the ETSI
Drafting Rules.
• Clear distinction between measurable quantities and associated statistical aggregations.
• Unambiguous naming of trigger events which occur in the definitions of several different QoS parameters.
• Systematic introduction and definition of appropriate points of observation which form the link between
harmonized, abstract QoS parameter definitions and their application to specific contexts, e.g. particular types
of access networks.
ETSI
7 ETSI TS 102 250-8-1 V1.1.1 (2018-12)
Over the years, application and maintenance of ETSI TS 102 250-2 [i.1] has revealed some deficiencies in this respect,
which are not easily solvable via ordinary change requests, but would require structural changes of ETSI
TS 102 250-2 [i.1]. Therefore, a new part 8 of the ETSI TS 102 250 series is introduced, of which the present document
represents the first sub-part.
The present document treats the aspects listed above in a systematic way and specifies general requirements for a
formalized definition of QoS parameters. Subsequent sub-parts of ETSI TS 102 250-8 are envisaged to contain QoS
parameter definitions in accordance with the present document. These definitions will then replace, and thus obsolete,
corresponding parts of ETSI TS 102 250-2 [i.1].
Clause 4 introduces the basic terminology used in a formalized treatment of QoS parameters: After clarifying the
difference between measurable quantities and statistical averages, the concept of points of observation is explained in
detail. Afterwards, the notion of abstract and technical events is introduced and used to specify a methodology for
deriving harmonized QoS parameters in two stages. Finally, a formalized, event-based characterization of the term
"transaction" is given, which proves to be useful when modelling complex scenarios of service usage.
Clause 5 specifies generic symbols and formulas for types of quantities frequently occurring in QoS parameter
definitions, like event indicators, time durations or data rates. In addition, formally correct definitions for commonly
used sample averages are given.
A systematic approach for deriving QoS parameters for non-trivial services, which may be subdivided into different
"phases", is outlined in clause 6.
Finally, clause 7 defines user-oriented points of observation for different types of access networks. The exact locations
of these points are illustrated in protocol stack overview figures, and reference is made to the corresponding protocol
specifications.
Two informative annexes complement the main text of the present document:
• Annex A gives some guidance how to apply the rather formal definitions of clause 5 in practice by outlining a
contrived, but complete, example.
• Annex B contains guidelines for writing specifications according to the present document. These guidelines
include suggestions for structuring the respective document (for example, one of the intended further sub-parts
of ETSI TS 102 250-8 [i.3]) as well as templates for particular parts of such specifications.

ETSI
8 ETSI TS 102 250-8-1 V1.1.1 (2018-12)
1 Scope
The present document defines a consistent terminology for the formalized definition of quality of service (QoS)
parameters and their computation. In doing so, it carefully distinguishes between measurable quantities and associated
statistical aggregation formulas. For frequently used types of quantities and aggregations, generic symbols and
calculation formulas are specified.
For a large class of QoS parameters, which are basically determined by the observation of events, the present document
specifies a methodology for constructing definitions in two stages, using the concept of abstract events and their
representation by technical events at well-defined points of observation.
In addition, a framework is presented which indicates how QoS parameters may be derived in a generic way via sub-
dividing the usage of a service into meaningful sub-transactions, called "phases".
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
https://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are necessary for the application of the present document.
[1] ETSI TS 102 250-6: "Speech Processing, Transmission and Quality Aspects (STQ); QoS aspects
for popular services in GSM and 3G networks; Part 6: Post processing and statistical methods".
[2] ETSI TS 102 250-7: "Speech and multimedia Transmission Quality (STQ); QoS aspects for
popular services in GSM and 3G networks; Part 7: Network based Quality of Service
measurements".
[3] ETSI TS 124 002: "Digital cellular telecommunications system (Phase 2+) (GSM); Universal
Mobile Telecommunications System (UMTS); LTE; GSM - UMTS Public Land Mobile Network
(PLMN) Access Reference Configuration (3GPP TS 24.002)".
[4] ETSI TS 143 051: "Digital cellular telecommunications system (Phase 2+); Overall description;
Stage 2 (3GPP TS 43.051)".
[5] ETSI TS 123 060: "Digital cellular telecommunications system (Phase 2+) (GSM); Universal
Mobile Telecommunications System (UMTS); General Packet Radio Service (GPRS); Service
description; Stage 2 (3GPP TS 23.060)".
[6] ETSI TS 123 401: "LTE; General Packet Radio Service (GPRS) enhancements for Evolved
Universal Terrestrial Radio Access Network (E-UTRAN) access (3GPP TS 23.401)".
[7] ETSI TS 127 007: "Digital cellular telecommunications system (Phase 2+) (GSM); Universal
Mobile Telecommunications System (UMTS); LTE; AT command set for User Equipment (UE)
(3GPP TS 27.007)".
[8] ETSI TS 127 060: "Digital cellular telecommunications system (Phase 2+) (GSM); Universal
Mobile Telecommunications System (UMTS); LTE; Packet domain; Mobile Station (MS)
supporting Packet Switched services (3GPP TS 27.060)".
[9] IETF RFC 3501: "Internet message access protocol - version 4rev1".
ETSI
9 ETSI TS 102 250-8-1 V1.1.1 (2018-12)
[10] IETF RFC 1939: "Post Office Protocol - Version 3".
[11] IETF RFC 5321: "Simple Mail Transfer Protocol".
[12] IEEE Std 802.11™: " IEEE Standard for Information technology - Telecommunications and
information exchange between systems Local and metropolitan area networks - Specific
requirements - Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)
Specifications".
[13] IETF RFC 1034: "Domain names - concepts and facilities".
[14] IETF RFC 1035: "Domain names - implementation and specification".
[15] IETF RFC 959: "File Transfer Protocol".
[16] IETF RFC 3261: "SIP: Session Initiation Protocol".
[17] IETF RFC 3550: "RTP: A Transport Protocol for Real-Time Applications".
[18] IETF RFC 3711: "The Secure Real-time Transport Protocol (SRTP)".
[19] IETF RFC 7826: "Real-Time Streaming Protocol Version 2.0".
[20] IETF RFC 7230: "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing".
[21] IETF RFC 2131: "Dynamic Host Configuration Protocol".
[22] ETSI EN 300 392-5: "Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D) and Direct
Mode Operation (DMO); Part 5: Peripheral Equipment Interface (PEI)".
[23] ETSI TS 144 001: "Digital cellular telecommunications system (Phase 2+); Mobile Station - Base
Station System (MS - BSS) interface; General aspects and principles (3GPP TS 44.001)".
[24] ETSI TS 144 004: "Digital cellular telecommunications system (Phase 2+) (GSM); GSM/EDGE
Layer 1; General Requirements (3GPP TS 44.004)".
[25] ETSI TS 144 005: "Digital cellular telecommunications system (Phase 2+) (GSM); GSM/EDGE
Data Link (DL) Layer; General aspects (3GPP TS 44.005)".
[26] ETSI TS 145 008: "Digital cellular telecommunications system (Phase 2+) (GSM); GSM/EDGE
Radio subsystem link control (3GPP TS 45.008)".
[27] ETSI TS 124 007: "Digital cellular telecommunications system (Phase 2+) (GSM); Universal
Mobile Telecommunications System (UMTS); LTE; Mobile radio interface signalling layer 3;
General Aspects (3GPP TS 24.007)".
[28] ETSI EN 300 392-1: "Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D); Part 1:
General network design".
[29] ETSI EN 300 392-2: "Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D); Part 2: Air
Interface (AI)".
[30] ETSI TS 125 301: "Universal Mobile Telecommunications System (UMTS); Radio interface
protocol architecture (3GPP TS 25.301)".
[31] ETSI TS 124 301: "Universal Mobile Telecommunications System (UMTS); LTE; Non-Access-
Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3 (3GPP TS 24.301)".
[32] ETSI TS 136 331: "LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource
Control (RRC); Protocol specification (3GPP TS 36.331)".
[33] Recommendation ITU-T I.411: "ISDN user-network interfaces - Reference configurations".
[34] Recommendation ITU-T I.412: "ISDN user-network interfaces - Interface structures and access
capabilities".
ETSI
10 ETSI TS 102 250-8-1 V1.1.1 (2018-12)
[35] Recommendation ITU-T Q.931: "ISDN user-network interface layer 3 specification for basic call
control".
[36] ETSI TS 102 250-1: "Speech and multimedia Transmission Quality (STQ); QoS aspects for
popular services in mobile networks; Part 1: Assessment of Quality of Service".
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] ETSI TS 102 250-2: "Speech and multimedia Transmission Quality (STQ); QoS aspects for
popular services in mobile networks; Part 2: Definition of Quality of Service parameters and their
computation".
[i.2] Recommendation ITU-T X.290: "OSI conformance testing methodology and framework for
protocol Recommendations for ITU-T applications - General concepts".
[i.3] ETSI TS 102 250-8 (all sub-parts): "Speech and multimedia Transmission Quality (STQ); QoS
aspects for popular services in mobile networks; Part 8: Formalized definition of Quality of
Service parameters and their computation".
3 Definitions of terms, symbols and abbreviations
3.1 Terms
For the purposes of the present document, the following terms apply:
abstract event: abstractly formulated proposition, which can be said to be either true or false
point of observation: combination of a particular reference point with a particular protocol layer or service access point
at that reference point
technical event: observation that a well-defined piece of data has been either sent or received
3.2 Symbols
For the purposes of the present document, the following symbols apply:
≔ "is defined by" operator stating that the quantity on its left-hand side is defined by the expression
on its right-hand side
data rate of a data transfer transaction T

mean data rate of a data transfer transaction T
∆ duration of a transaction
∆ mean duration of a transaction
∆ amount of data transferred in a transaction

event defining the end of a transaction
,
event defining the start of a transaction
,
success condition of a transaction
,
indicator of an event
() number of measurement cycles where an event has occurred
ETSI
11 ETSI TS 102 250-8-1 V1.1.1 (2018-12)
measurable quantity
sample average of a measurable quantity
| sample average of a measurable quantity under the condition that an event has occurred
() sample ratio of an event
(|) sample ratio of an event under the condition that an event has occurred
failure ratio of a transaction
,
success ratio of a transaction
,
transaction
time of occurrence of an event
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
API Application Programming Interface
AT ATtention command prefix
CLI Calling Line Identification
CMCE Circuit Mode Control Entity
CR Change Request
CS Circuit Switched
DHCP Dynamic Host Configuration Protocol
EDGE Enhanced Data rates for GSM Evolution
FTP File Transfer Protocol
GERAN GSM/EDGE Radio Access Network
GSM Global System for Mobile communications
HTTP Hyper Text Transport Protocol
ISDN Integrated Services Digital Network
LLC Logical Link Control
MAC Medium Access Control
MLME MAC subLayer Management Entity
MMI Man Machine Interface
MMS Multimedia Messaging Service
MOS Mean Opinion Score
MS Mobile Station
MT Mobile Termination
n.a. not available
PCO Point of Control and Observation
PO Point of Observation
PPP Point-to-Point Protocol
PS Packed Switched
QoS Quality of Service
RT Reference point between TE and MT in TETRA
RTP Realtime Transport Protocol
RTCP Realtime Transport Control Protocol
RTSP Real Time Streaming Protocol
SIM Subscriber Identity Module
SIP Session Initiation Protocol
SME Station Management Entity
SNDCP SubNetwork Dependant Convergence Protocol
TA Terminal Adapter
TE Terminal Equipment
TETRA TErrestrial Trunked RAdio
UE User Equipment
UMTS Universal Mobile Telecommunications Service
UNI User Network Interface
UTRAN Universal Terrestrial Radio Access Network
XML eXtensible Markup Language
ETSI
12 ETSI TS 102 250-8-1 V1.1.1 (2018-12)
4 QoS parameter basics
4.1 Measurable quantities and sample averages
The document series ETSI TS 102 250-8 [i.3] defines QoS parameters as quantitative measures for particular quality
aspects of popular services in mobile networks. The definition of such a quantitative measure shall consist of two parts:
1) A measurable quantity Q associated with the respective QoS parameter shall be defined. This means, an
explicit equation or algorithm shall be given which represents a unique instruction how to determine the
measured value of the respective QoS parameter from more elementary observation data (like events, speech
samples, etc.) in a single measurement.
2) An aggregation formula or algorithm shall be specified which maps a set {,…,} of results of repeated
measurements of the same quantity Q to a single value. This aggregated value then provides the desired
measure associated with the respective QoS parameter.
The rationale behind this approach is the following: Mobile networks are complex dynamical systems, whose state
undergoes non-systematic fluctuations on small time scales (in fact, the same is true not only for mobile networks, but
for any telecommunication network). Possible origins of these fluctuations are varying radio conditions, varying
utilization by different users and many other factors.
Due to this fluctuating behaviour, a single measurement of any quantity representing a QoS aspect (e.g. the time needed
to set up a particular telephony call) usually does not yet yield a meaningful measure for this QoS aspect: Repeated
measurements of the same quantity will in general yield different results which may exhibit considerable variations,
even while there is no systematic change in the network conditions.
NOTE: These variations have their origin in the incomplete control over the state of the network (it is practically
impossible to know all the parameters influencing this state) and should not be confused with
uncertainties introduced by the measurement equipment - the variations would be present even if
measured with an ideal, error-free measurement device. Of course, any real measurement system will add
yet another contribution (to be kept as small as possible) to the variability of the results.
In order to deal with the fluctuating nature of a mobile network, a statistical approach is taken: The same quantity is
measured repeatedly, and statistical aggregation of the single results will then provide the desired measure. Loosely
speaking, statistical aggregation will "cancel out" non-systematic fluctuations of the single measurement results in
favour of statistically relevant information, like mean or median values, variances, percentiles, etc.
A frequently used aggregation of a set of N measurement results {,…,} for the same quantity Q is the arithmetic
mean of the result set, also called the "sample average":
∶= ∑ (4.1)
For specific purposes, other statistical aggregations, like median, quantiles, etc. may be used as well (for details please
refer to ETSI TS 102 250-6 [1]).
The reader should distinguish between the measurable quantity Q associated with a QoS parameter on the one hand,
and the sample average of this quantity on the other hand: The former comprises the elementary definition of the
QoS parameter by a measurement instruction, while the latter represents the proper measure (involving statistical
aggregation) associated with this QoS parameter.
Nevertheless, for the sake of simplicity, the term "QoS parameter" will be used in the present document with either
meaning whenever it is clear from the context that no ambiguity can arise.
Depending on the specific quality aspects to be reflected by a particular QoS parameter, the formula or algorithm
defining the corresponding measurable quantity Q may already involve aggregation itself (from yet more elementary
measurement data). However, this kind of aggregation still needs to be distinguished from the one employed to get
sample averages. In other words, the definition of the measurable quantity determines what is regarded to be a "sample"
in a particular context. Several alternatives may be possible, the choice being a matter of convenience.
ETSI
13 ETSI TS 102 250-8-1 V1.1.1 (2018-12)
Consider for example speech quality measures for telephony calls: In addition to a "speech quality on sample basis",
where the measurable quantity basically consists of a mean opinion score (MOS) for a single speech sample, another
QoS parameter "speech quality on call basis" may be introduced, where the definition of the measurable quantity
involves an aggregation over all speech samples in a particular call. In the former case, the sample space for statistical
calculations consists of as many values as there have been speech samples in all calls considered, whereas in the latter
case the number of statistical samples equals the number of calls.
4.2 Points of observation
To avoid ambiguities when defining QoS parameters in terms of measurable quantities, the definition of what is to be
measured shall be complemented with a precise specification of where (in the functional architecture of the
telecommunication network) the respective quantity shall be observed. Conversely, the specific representation of an
(abstractly chara
...